Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $207.98   3.779%   $215.8396   $215.84   $215.85   $215.80  
  Purchase #2 $22.83   4.682%   $23.8989   $23.90   $23.90   $23.90  
  Purchase #3 $230.54   10.725%   $255.2654   $255.27   $255.25   $255.30  
  Purchase #4 $229.70   10.450%   $253.7037   $253.70   $253.70   $253.70  
  Purchase #5 $126.75   7.210%   $135.8887   $135.89   $135.90   $135.90  
  Purchase #6 $39.82   11.162%   $44.2647   $44.26   $44.25   $44.30  
  Purchase #7 $111.80   9.684%   $122.6267   $122.63   $122.65   $122.60  
  7 purchase totals = $969.42       $1,051.4877   $1,051.49   $1,051.50   $1,051.50